barbzilla said:
The movie clearly shows him making the steel plates while he is on his lunch break at the auto shop, and I am aware of it being illegal to ship any type of firearm to a non-ffl licensed person. It never shows kevlar, but I, like you, assumed it was used as the base. Unfortunately kevlar doesn't stop much without the plates in it, but we will say that it did manage to stop the bullets, he would have still had broken ribs. While the rounds won't penetrate the armor (I mean police standard issue is 9mm so it would probably stop it) the kinetic energy is still going to have to be absorbed. Unfortunately cloth doesn't do that very well, so the body ends up absorbing that energy. In the scene in question he would not have walked away uninjured period, and that is assuming that his armor does work.
I assumed it had to be either the weapons or the ammo that was shipped to his friend's place to aid in the set up as you said. Steel plates are way too common and easy to obtain for that to have been any factor in securing proof. There is also the issue of their being zero response to the police station bombing. With a bombing of that size the national guard would have been there in hours, and the state law enforcement would have been there in less than an hour.
This is all besides the point though. Like I said, I enjoyed the movie and thought it was fairly well done. Those were my only issues, and it was only an issue as far as suspension of disbelief. I think that the errors that were made were done so with the intention of effect on the story, and as such it works perfectly.